This invention relates to a communications system including a central controller coupled to a plurality of remote transceiver modules by a serial bus and, more particularly, to such a system where the modules remain in a sleep mode without consuming any power until such time as the central controller provides a wakeup signal over the bus.
Systems are known which include a central controller and a plurality of remote transceiver modules communicating with the central controller over a bus. It is common in such a system that the remote transceiver modules are normally in a low power consuming standby mode and at regular intervals xe2x80x9cwake upxe2x80x9d to look for an interrogation signal placed on the bus by the central controller. If no such interrogation signal is recognized, the module returns to its standby mode. However, even while it is in a standby mode, the module consumes power. There are applications where such power consumption is undesirable. For example, in a system where the modules are utilized to monitor battery systems and each module receives its operating power from the batteries which it is monitoring, the aforedescribed approach results in unacceptable battery drain. Accordingly, it would be desirable to have a system of the type described wherein the remote modules do not consume any power whatsoever while in the standby mode.
According to the present invention, there is provided an electronic system having a central controller, at least one remote transceiver module, and a serial bus interconnecting the central controller and all of the remote transceiver modules. Each module includes a source of power and power supply circuitry adapted to provide power for operating the module when the power supply circuitry is connected to the source of power. The central controller is adapted to transmit energy along the bus as a signal to all of the modules to change state to an active mode from a sleep mode in which each module consumes no power. Each module further includes an energy detector coupled to the bus and adapted to connect the power supply circuitry to the source of power upon detection of energy on the bus.
In accordance with an aspect of this invention, the bus is a continuous twisted pair of wires coupled together at an end remote from the central controller. Each module includes a transformer having a ferrite core extending through the twisted pair of wires so that the primary winding of the transformer is a single turn of the bus wires, with the transformer further having a secondary winding coupled to the energy detector.
In accordance with another aspect of this invention, the power supply circuitry includes a transformer to provide galvanic separation between the source of power and the power provided by the power supply circuit.
Further according to this invention, each module includes a winding inductively coupled to the bus for selectively effecting communication between the module and the central controller, and each module is arranged to short its winding when that module is not communicating with the central controller. Accordingly, the bus is minimally loaded by those modules not communicating with the central controller.